Fusion pore formation and expansion induced by Ca2+ and synaptotagmin 1

Proc Natl Acad Sci U S A. 2013 Jan 22;110(4):1333-8. doi: 10.1073/pnas.1218818110. Epub 2013 Jan 8.


Fusion pore formation and expansion, crucial steps for neurotransmitter release and vesicle recycling in soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-dependent vesicle fusion, have not been well studied in vitro due to the lack of a reliable content-mixing fusion assay. Using methods detecting the intervesicular mixing of small and large cargoes at a single-vesicle level, we found that the neuronal SNARE complexes have the capacity to drive membrane hemifusion. However, efficient fusion pore formation and expansion require synaptotagmin 1 and Ca(2+). Real-time measurements show that pore expansion detected by content mixing of large DNA cargoes occurs much slower than initial pore formation that transmits small cargoes. Slow pore expansion perhaps provides a time window for vesicles to escape the full collapse fusion pathway via alternative mechanisms such as kiss-and-run. The results also show that complexin 1 stimulates pore expansion significantly, which could put bias between two pathways of vesicle recycling.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Vesicular Transport / metabolism
  • Animals
  • Biophysical Phenomena
  • Calcium / metabolism*
  • DNA Probes
  • Lipid Metabolism
  • Membrane Fusion / physiology*
  • Models, Biological
  • Models, Molecular
  • Mutagenesis, Site-Directed
  • Nerve Tissue Proteins / metabolism
  • Neurons / metabolism
  • Rats
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • SNARE Proteins / chemistry
  • SNARE Proteins / genetics
  • SNARE Proteins / metabolism
  • Synaptotagmin I / chemistry
  • Synaptotagmin I / genetics
  • Synaptotagmin I / metabolism*


  • Adaptor Proteins, Vesicular Transport
  • DNA Probes
  • Nerve Tissue Proteins
  • Recombinant Fusion Proteins
  • SNARE Proteins
  • Synaptotagmin I
  • Syt1 protein, rat
  • complexin I
  • Calcium